A number of different approaches to generate light from a solid state light emitting device are known.
A very common approach is to use light emitting diodes (LEDs), which are in increasing use for a number of applications in view of their efficiency in generating light. In order to use such LEDs, LED dies are packaged to protect the die while allowing light to be emitted and to allow electrical connection to the LED die. Since LEDs can generate considerable amounts of heat, such packages may also need to allow the removal of heat and hence function as a heat sink.
LED technology does not represent the only way to generate light in solid state devices. In particular, an alternative approach involves the use of laser diodes. A large number of types of laser diodes are known, including in particular vertical cavity surface emitting lasers (VCSEL), vertical external cavity surface emitting lasers (VECSEL), heterostructure lasers, distributed feedback lasers, and external-cavity diode lasers.
For lighting and backlighting applications, the use of VCSEL and VECSEL light emitting devices has been of particular interest. Such devices can efficiently emit light of a particular wavelength. The light emitted may be narrow band, which can be an advantage in some applications.
Where broad spectrum light, for example white light is required, this can be achieved from VCSEL and VECSEL type devices using phosphors. The reason for using phosphors with such devices is that there are technical difficulties in producing VCSEL and VECSEL devices with some wavelengths. One option is to use a blue VCSEL diode with a phosphor to create white light. However, the light emitted by such devices may be considered cold and it would therefore be beneficial to provide a warmer light color. These devices in particular are suitable for use in lighting applications.
A prior approach to packaging LEDs or other solid state light emitting devices is described by US2012/0313131. This document describes packaging an LED using an etched leadframe incorporated in a resin portion shaped to form the package body. The LED is mounted on the leadframe and connected to it either with wire bonding or with bump bonding. A reflective metal layer on the upper surface of the leadframe reflects light and hence increases illumination efficiency of the packaged LED.
A typical metal for such a reflective metal layer is silver. This may be prone to degradation in the form of tarnishing which can color the reflective metal layer and lead to reduced reflectivity. A further issue is the weak adhesion of mould compound to Ag leading to delamination risks.
Another approach to packaging an LED is provided by US2013/0026522. This document describes a leadframe with a silver coating combined with a resin package body. The resin package body is formed of a heat curable resin with reflective properties. In this way, light incident not only on the leadframe but also on the resin is reflected to improve illumination efficiency.
However, this package has a relatively simple structure. Although this may make manufacture of the package more straightforward assembly of the package requires additional wirebonding steps.
Other reflective resins used in a similar way in LED packaging are provided by US2011/0241048 and US2012/0286220.
US2013/0221509A1 discloses a leadframe for mounting LED elements which includes a frame body region and a large number of package regions arranged in multiple rows and columns in the frame body region. The package regions each include a die pad on which an LED element is to be mounted and a lead section adjacent to the die pad, the package regions being further constructed to be interconnected via a dicing region.
There therefore remains a need for an improved packaged light emitting device which is relatively straightforward to manufacture and which allows for ease of assembly of a die into the package body.